A jump playback function is to start playback of a digital stream encoded by variable-length coding, from a randomly chosen point in the digital stream. In the case of a video stream encoded using the MPEG2-Video or MPEG4-AVC standard, execution of jump playback requires that all the pictures referenced by a picture located at a jump playback point be supplied to the decoder. How much of the video stream needs to be read in order to supply all the necessary reference pictures to the decoder varies depending on the structure of the GOPs contained in the video stream. An MPEG2-Video stream contains different types of GOPs, such as closed-GOPs and open-GOPs. A closed-GOP uses no reference pictures from any other GOP. Thus, by reading the video stream from a closed-GOP containing a jump playback point, all the necessary reference pictures will be supplied to the decoder.
Taking an MPEG2-Video stream as an example, an open-GOP has references not only within the GOP itself but also from an immediately previous GOP. Consequently, in order to execute jump playback from an open-GOP, the playback apparatus needs to start reading the recording medium from the GOP that immediately previous to the target open-GOP and supply the read GOP to the decoder. That is, in order to start playback from an open-GOP, the playback apparatus is required to read the GOP immediately previous to the target open-GOP.
For executing jump playback, it is necessary to detect an I (Intra) picture located at the start of a GOP. The following patent literature discloses the data structure facilitating I picture detection.
Patent Literature 1: JP Patent Application Publication No. 2001-169247 (Application No. 2000-228656)